As police continue to search Boston for Dzhokhar Tsarnaev, the 19-year-old believed to be partly responsible for the Boston Marathon bombings along with his older brother Tamerlan, a key question remains unanswered: What motivated the brothers?

Each of them has left possible clues online.

Tamerlan, who was killed in a shootout earlier today, appears to have been sympathetic to Islamist radicalism. Five months ago, he appears to have created a channel on YouTube called Terrorists. The channel features videos from the one of the leaders of the insurgency in Dagestan, who goes by the name Amir Abu Dudzhan. YouTube appears to have removed two of the videos but in a third features Dudzhan calling for jihad. Holding a Kalashnikov rifle, he says, “Jihad is the duty of every able-bodied Muslim.” Among the other videos on his channel is one of Timur Mutsuraev, the bard of the Chechen resistance in the 1990s; it features his song “We Will Devote Our Lives to Jihad.”

The younger brother, Dzhokhar, attended school from 1999 to 2001 in the Russian republic of Dagestan, a war-torn part of Russia next to Chechnya, according to his page on the Russian social-networking site Vkontakte. But even though Dzhokhar’s page indicates an interest in conflicts and causes that have at times been connected to terrorism, no solid evidence has emerged to suggest that he is motivated by religious or nationalist causes.

On his Vkontakte page he posted video messages sympathetic to the cause of Chechen independence — but Chechen independence from Russia is a cause that has the support of secular as well as Islamist activists. He also expresses sympathy for rebel fighters in Syria and elsewhere. One video bears the Russian title For Those Who Have a Heart. It shows people being brutalized by uniformed men in a country the video identifies as Syria. “They are killing your brothers and sisters without any reason,” the Russian subtitles of the video read. “Simply because they say our Lord is Allah.” The conflict in Syria, however, is almost entirely fought by Muslims on both the rebel and government sides—although the war is increasingly marked by sectarianism, with the Sunni Muslim majority making up the bulk of the rebel forces and the Alawite minority generally supporting the government of Bashar Assad.

Another video on his page seems at first glance to suggest a sympathy for Salafi Islam, an extreme form of Sunni Islam. The video is posted from a blog named Salyafi Street — but it turns out to be about a young blind boy who thanks God for his blindness because it will mean greater mercy for him when God’s judgment comes.

Such videos are relatively common among Muslim youth throughout Russia — and in the ethnic Chechen diaspora — and Tsarnaev’s page contains much lighter fare as well. It features clips from a Russian sketch comedy show that plays on the accents of men from Chechnya and other regions of the Russian Caucasus. In many ways, the page seems to be that of a normal ethnically Chechen kid.

It’s unclear when Dzhokhar left the Caucasus region and moved to the U.S. An uncle told CNN that the family lived for some time in Kyrgyzstan before moving to the U.S. According to classmates interviewed by CNN, he went to high school in Cambridge and worked at Harvard University. One of his acquaintances recalled a conversation Dzhokhar had with a classmate during which Dzhokhar allegedly said, “In relation to acts of terrorism, he said it was not a serious issue if you come from a place where I come from,” the acquaintance, Eric Machado, told CNN. “Those comments raised a red flag in my head.”

In 2011, Dzhokhar appears to have won a city of Cambridge scholarship of $2,500. In February 2011 he was the Cambridge student of the month for his wrestling prowess; wrestling is the national pastime of Chechnya and the Caucasus.

The Associated Press spoke to Dzhokhar’s father, who was in the Russian city of Makhachkala, which is the capital of the Russian republic of Dagestan. “My son is a true angel,” Anzor Tsarnaev told the AP. In a separate interview with the Russian news agency Interfax, their father said, “Dzhokhar is a second-year medical student in the U.S. He is such an intelligent boy. We expected him to come on holidays here.”